Conan, Masumi, Sonoko, and Ran go buy swimsuits in an upscale apartment store. The girls spend a while trying on many two-pieces, which causes Conan to remember something from the past.

As goes out for a stroll to clear his mind. Conan witnesses the extremely bitchy behavior of a rich woman named Ritsuko Sashihara. She belittles and abuses another client (Tomoyo), the shop assistant in charge (Reia) and her assistant Ayami. Few later, Ritsuko is found strangled to death and bleeding in the dressing room. Conan and Masumi check on the corpse and realize that she left some dying clues, and Conan recalls more and more of the old incident that he's been thinking about through the shopping trip.

The culprit is Ayami Yamaki, Ritsuko Sashihara's assistant. She did it because she had been humiliated by the victim when she dress her dog in the same outfit as Yamaki. When she saw that, Yamaki understood that she was a slave to her boss and wanted to leave the company, but couldn't since she was in massive debt to her cruel boss. She became so desperate that she decided to kill Ritsuko to free herself.

Conan thinks about how Masumi didn't know the difference between how Americans and Japanese count and how Europeans count, and connects it to other instances of Masumi saying and doing things that someone who lived in America wouldn't—being surprised at how thin a baseball bat was, and keeping her fork in her left hand while eating during the Red Woman case, and referring to soccer as "football" during the Romance Novelist case. Conan realizes that these instances show that Masumi actually lived in the United Kingdom, not in the United States, in Britain, cricket is more popular than baseball and has a wider bat, when eating, one would not switch the fork to the right hand, as is the case in the United States, and the British refer to association football as "Football", while in the U.S. it's called "Soccer".

As Conan wonders why Masumi would lie about this, he begins to think of England, and finally remembers something. He and Ran did meet Masumi before, several years ago, alongside other people.

Because the three manga chapters were not enough to make two episodes, some scenes were either made longer, or dialogues were added.

During her interrogation scene, Ayami is asked about the gifts in her purse. She tells the police that the boxes contain perfume and are a gift for the store manager. In the manga, Takagi requests to see the contents of her perfumes boxes. In the anime, however, Ayami herself offers to show him.